Some tire condition monitoring systems for vehicles have pressure sensors and transmitters mounted on tire wheels, respectively, and receivers mounted on wheel houses, respectively. In this system, the pressure sensors periodically detect air pressures in the tires as tire information and the transmitters transmit the tire information to the receivers, respectively, when a predetermined condition defined by pressure changes, times or the like holds.
Other tire condition monitoring systems further have transmitters on the wheel houses to transmit trigger signals from the chassis side and receivers on the tire wheels, so that the transmitters on the tire side transmit the tire information in response to the trigger signals from the chassis side.
In the latter systems, in which bi-lateral communications are attained between the chassis side and the tire side, a communication range is limited to be less than an entire periphery (360°) due to communication regulations, power consumption or the like. The communication is enabled only when the tire-side transmitter/receiver enters the limited communication range of the chassis-side transmitter/receiver. This results in low rate of reception of the tire information. Since the communication period becomes shorter as the vehicle travels at higher speeds, the communication rate becomes further low. In the case in which the tire-side transmitter/receiver receives electric power from the chassis side, the period for receiving the electric power from the chassis side becomes shorter as the vehicle travels at higher speeds, thus resulting in insufficient power reception from the chassis side.